Fibrous products are used for a variety of purposes. Paper towels, facial tissues, toilet tissues, and the like are in constant use in modem industrialized societies. The large demand for such fibrous products, including paper products, has created a demand for improved versions of the products. If the paper products such as paper towels, facial tissues, toilet tissues, and the like are to perform their intended tasks and to find wide acceptance, they must possess certain physical characteristics. Among the more important of these characteristics are strength, softness, and absorbency.
Strength is the ability of a fibrous web to retain its physical integrity during use.
Softness is the pleasing tactile sensation consumers perceive when they use the fibrous product for its intended purposes.
Absorbency is the characteristic of the fibrous product that allows the product to take up and retain fluids, particularly water and aqueous solutions and suspensions. Important not only is the absolute quantity of fluid a given amount of the product will hold, but also the rate at which the product will absorb the fluid.
Fibrous structures currently made by the present assignee contain multiple micro-regions defined by differences in density and/or basis weight. The more typical differential density cellulosic structures are created by first, an application of vacuum pressure to the wet web associated with a molding belt thereby deflecting a portion of the papermaking fibers--to generate the low density regions, and second, pressing portions of the web comprising the non-deflected papermaking fibers against a hard surface, such as a surface of a Yankee dryer drum,--to produce the high density regions. High density micro-regions of such cellulosic structures generate strength, while low density micro-regions contribute softness, bulk and absorbency.
Such differential density cellulosic structures may be produced using through-air drying papermaking belts comprising a reinforcing structure and a resinous framework, which belts are described in commonly assigned U.S. Pat. No. 4,514,345 issued to Johnson et al. on Apr. 30, 1985; U.S. Pat. No. 4,528,239 issued to Trokhan on Jul. 9, 1985; U.S. Pat. No. 4,529,480 issued to Trokhan on Jul. 16, 1985; U.S. Pat. No. 4,637,859 issued to Trokhan on Jan. 20, 1987; U.S. Pat. No. 5,334,289 issued to Trokhan et al on Aug. 2, 1994. The foregoing patents are incorporated herein by reference.
There is a well-established relationship between strength and density of a fibrous web. Therefore, the efforts have been made to produce highly densified fibrous webs. One of such methods, known as CONDEBELT.RTM. technology, is disclosed in the U.S. Pat. No. 4,112,586 issued Sep. 12, 1978; the U.S. Pat. Nos. 4,506,456 and 4,506,457 both issued Mar. 26, 1985; U.S. Pat. No. 4,899,461 issued Feb. 13, 1990; U.S. Pat. No. 4,932,139 issued Jun. 12, 1990; U.S. Pat. No. 5,594,997 issued Jan. 21, 1997, all foregoing patents issued to Lehtinen; and U.S. Pat. No. 4,622,758 issued Nov. 18, 1986 to Lehtinen et al.; U.S. Pat. No. 4,958,444 issued Sep. 25, 1990 to Rautakorpi et al. All the foregoing patents are assigned to Valmet Corporation of Finland and incorporated by reference herein. The CONDEBELT.RTM. technology uses a pair of moving endless bands to dry the web which is pressed and moves between and in parallel with the bands. The bands have different temperatures. A thermal gradient drives water from the relatively heated side, and the water condenses into a fabric on the relatively cold side. A combination of temperature, pressure, moisture content of the web, and residence time causes the hemicelluloses and lignin contained in the papermaking fibers of the web to soften and flow, thereby interconnecting and "welding" the papermaking fibers together.
While the CONDEBELT.RTM. technology allows production of a highly-densified strong paper suitable for packaging needs, this method is not adequate to produce a strong and--at the same time--soft fibrous products such as facial tissue, paper towel, napkins, toilet tissue, and the like.
Therefore, it is a purpose of the present invention to provide a novel process for making a strong, soft, and absorbent fibrous structures comprising at least two micro-regions: micro-regions formed by the fibers which are interconnected by the fiber-binding substance, and micro-regions which are not interconnected by the fiber-binding substance. It is still another object of the present invention to provide a fibrous structure having a plurality of micro-regions comprising fibers interconnected by the fiber-binding substance.
It is another object of the present invention to provide an apparatus for making such a fibrous web.